Packaging containers or cartons of the single-use disposable type are often produced from a packaging material of the above-disclosed type. The packaging material is most generally provided in the form of webs rolled onto magazine reels and which, after unreeling from their magazine reels are reformed by folding into packaging containers or cartons. A package of this type which is common in the market place is that which is marketed under the trademark Tetra Brik.RTM., and which is primarily employed for liquid contents such as milk, fruit juice etc. This package is produced in automatic packaging and filling machines in such a manner that the web unreeled from the magazine reel is reformed into a tube in that the edges of the web are united in an overlap joint or seam, whereafter the thus formed tube is filled with the intended contents and divided into individual packages with the aid of repeated transverse seals disposed in spaced apart relationship and at right angles to the tube. Once the supplied contents have been enclosed by such means in sealed parts of the tube, these are separated from the tube by cutting through the above-mentioned transverse seal zones. The separated tube parts are thereafter formed by folding along crease lines provided in the packaging material into parallelepipedic packages.
Packages of this type are often provided with opening arrangements in the form of holes, apertures or slits made in the packaging material and covered with tear-off strips, so-called "pull-tabs", and when the contents consist of a sterile product such as, for instance, sterilized milk or of an acidic product such as, for example, orange juice, the package is often manufactured from a packaging laminate including an aluminium foil layer which renders the package extremely tight against penetration by gases such as, for example, oxygen gas. In order to achieve the desired tightness, it is of crucial importance that the aluminium foil layer is not ruptured or damaged when the package is formed or on manufacture of the packaging material and, for the function of the pull-tab opening, it is vital that the aluminium foil layer possess extremely good adhesion in the region about the opening hole or aperture over which the tear-off strips are intended to be applied in a manner which will be described in greater detail hereinbelow.
A further object of the present invention is to treat and prepare, in a simple and efficient manner, a packaging material web of the above-mentioned type in such a way that the edge of the packaging material web is efficiently sealed-off with a plastic film disposed over or about the edge zone. It is known to seal-off liquid-absorbing material edges exposed to the inside of a packaging container with thermoplastic strips which bridge over or are folded around the edges. For the same purpose, it is also known in the art to provide the packaging material web with a so-called fixed edge strip of plastic, i.e. with a plastic strip which projects out from the rear edge of a board web and which can be folded around the edge and sealed against the opposing side. Such a "fixed edge strip" is obtained by disposing board webs in side-by-side relationship so that they form therebetween a slit or a gap, whereafter the webs and the slits are jointly covered over with a plastic foil or, in certain cases, with a plastic foil and an aluminium foil, whereafter the covered webs are separated by means of an incision in the slit zone, for forming a projecting, fixed strip. One inconvenience in this context has hitherto been that it has not proved possible to achieve adhesion (or in any event very poor adhesion) between, for example, an aluminium foil layer and a plastic layer in the region of the slits themselves, since these material webs cannot be compressed together within the slit zone because there is no backing support. Employing the method according to the present invention, it will, however, be possible to obviate this drawback by first producing a plastic-aluminium foil laminate in which the components in the laminate possess good adhesion to one another, and then laminate this plastic-aluminium foil laminate to the above-mentioned webs of core layer material, i.e. board, disposed side by side.
Packaging material of the type contemplated here can be produced using prior art technology by applying, in a plurality of separate lamination operations, the different layers, i.e. the aluminium foil layer, the inner plastic layer and so on, to the core layer of paper or board, and such a lamination process functions excellently in those cases when the core layer is not provided with holes, apertures or slits, i.e. regions where the coating layers extend over or beyond edge zones of the core layer. It has proved that, on coating of an aluminium foil against a core layer web of paper or board where the core layer is provided with holes, apertures or slits, difficulties occur in that the aluminium foil must, in connection with the lamination where the cohesive laminating layer most generally consists of a thin extruded thermoplastic film, be forced against the core layer substrate with the aid of a nip roller or soft pressure roller in order to achieve sufficient adhesion between the aluminium foil layer and the core layer. Since, as a rule, the aluminium foil layer is extremely thin (of the order of 5-10 .mu. meter), it will be forced by the nip roller against the edges around the apertures or slits in the core layer and partly pressed into these holes or apertures. Since the punched holes have a relatively sharp edge, there is a risk that the aluminium foil be ruptured and, at any rate, there is the risk that the aluminium foil will fold itself around the edges of the apertures or slits and will thereby either be weakened or suffer from inferior adhesion between the aluminium foil and the core layer precisely in the edge zones of the holes or apertures. Furthermore, adhesion between the plastic layer and the aluminium foil layer will be poor in the region of these holes or slits, since the pressure of the nip roller in these regions is limited.
The above-outlined circumstances have constituted a major problem which has, first, caused ruptures in the aluminium foil layer (and thereby insufficient gas tightness of the resultant packages), secondly, defective opening function because of poor adhesion between the aluminium foil layer and the core layer in the edge zones about the apertures, and thirdly poor adhesion between the aluminium foil layer and the plastic layer along those parts where the aluminium foil layer and the plastic layer project out beyond the core layer and, hence, are not supported by the core layer.
The above-considered drawbacks are obviated in an efficient manner by means of the present invention which is characterized in that an aluminium foil is fed in between a cooled roller and a first nip roller abutting against the cooled roller; that one or more thermoplastic materials in the molten or semi-molten state are extruded in the form of a continuous first film in between the cooled roller and the first nip roller in such a manner that the extruded first film is accommodated between the aluminium foil and the cooled roller, the thermoplastic material being, by cooling, stabilised and solidified at the same time as it is caused to adhere to the aluminium foil for the formation of a plastic-aluminium foil laminate; that this plastic-aluminium foil laminate is, under abutment against the cooled roller, led in under a second nip roller over which the webs of paper or board prepared with punched holes, apertures or slits are led and by means of which these webs are urged against the plastic-aluminium foil laminate passed over the cooled roller; that one or more thermoplastic materials in the molten or semi-molten state are extruded in the form of a continuous, second film in between the cooled roller and the second nip roller in such a manner that the extruded second film is accommodated between the aluminium foil side of the plastic-aluminium foil laminate and the paper or board web, the molten thermoplastic material in the second thermoplastic film being caused, by cooling, to stabilise and solidify at the same time as it is caused to adhere to both the aluminium foil side of the plastic-aluminium foil laminate and the paper or board web.